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Self-folding structures

‘Peel-and-go’ 3D structures self-fold into useful shapes

Image credit: MIT CSAIL

A team at Massachusetts Institute of Technology (MIT) has created simple printed structures which fold themselves into useful 3D structures without any external stimulus.

In an unusual marriage between cutting-edge technology and the traditional Japanese art of origami – ornamental paper folding – there has been an emergence of electronic devices (including basic robots) which only assume their final shape when folded.

These structures typically require heat, submergence in water, a small electrical current, or other external stimuli in order to assemble.

However, researchers at MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) have created small, printable structures capable of self-folding into useful shapes the moment they are peeled from the printing platform, with no need for heat or moisture.

“If you want to add printed electronics, you’re generally going to be using some organic materials, because a majority of printed electronics rely on them,” said Subramanian Sandaram, first author of the study and an MIT postgraduate.

“These materials are often very, very sensitive to moisture and temperature. So if you have these electronics and parts, and you want to initiate folds in them, you wouldn’t want to dunk them in water or heat them, because your electronics are going to degrade.”

The researchers built a prototype device, which is printed in the shape of a capital letter “H”. When lifted from the printing platform, the legs fold in different directions, producing the approximate shape of a table. These structures were able to bounce back to their 3D shape even after being flattened with a weight.

Key to this achievement of self-folding is a new printable material which expands after drying: most printer-ink materials contract instead. This material was discovered inadvertently when the CSAIL researchers mixed a combination of polymers, and were inspired by the discovery that it expands after solidification.

The material was printed into joints in the top and bottom layers of the printed structure. When the completed device is peeled off like a sticker, the bottom layer no longer adheres to the platform and the joints begin to expand, bending the entire structure into shape.

The researchers went on to build different versions of the same hinge design, adapting the angle at which the joints fold.

According to the CSAIL team, this could open up possibilities to include a wider range of materials and more delicate structures. The technique could enable the custom manufacture of sensors, displays and antennae with functions dependent on their shape, or even printable robots.

Earlier this year, researchers from Jilin University, China, unveiled basic robots which could be made to “crawl” with no external power source. With changing humidity, parts of the robot’s body were made to expand and contract, resulting in a crawling motion.

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